This invention relates to tool inserts and more particularly to tool inserts which comprise composite abrasive compacts.
A composite abrasive compact comprises an abrasive compact bonded to a cemented carbide support or substrate. The abrasive compact will invariably be a diamond or cubic boron nitride abrasive compact. Bonding between the abrasive compact and the substrate may be direct or through the medium of an interposed bonding layer.
Diamond abrasive compacts of such composite abrasive compacts consist of a layer of polycrystalline diamond (abbreviated often to PCD) which is made by subjecting individual diamond crystals to temperature and pressure conditions at which the diamond is crystallographically stable and at which direct diamond-to-diamond bonding occurs. A diamond solvent/catalyst second phase may be present to assist in the formation of the diamond-to-diamond bonding.
Composite abrasive compacts are extensively described in the patent literature and have been in commercial use for over a decade. Examples of patent specifications which describe and illustrate composite abrasive compacts are U.S. Pat. Nos. 3,743,489, 3,767,371, 4,063,909 and 3,745,623. U.S. Pat. No. 4,403,015 also describes a particular type of composite abrasive compact. This composite abrasive compact consists of a diamond or cubic boron nitride abrasive compact bonded to a cemented carbide substrate through an intermediate bonding layer less than 2 mm in thickness and comprising cubic boron nitride in an amount effective to ensure rigid bonding between the hard sintered compact and the cemented carbide substrate, but not exceeding 70 volume percent, the residual part consisting of a compound selected from the group consisting of carbides, nitrides, carbonitrides or borides of 4A, 5A, 6A transition metals of the Periodic Table, an admixture thereof, or a mutual solid solution compound thereof. The intermediate bonding layer may also contain aluminium and/or silicon and perhaps a minor quantity of binder metal such as cobalt from the cemented carbide substrate.
U.S. Pat. No. 4,604,106 describes a composite abrasive compact comprising an abrasive compact bonded to a cemented carbide support through an intermediate layer which comprises a mixture of diamond crystals and pre-cemented carbide pieces. The carbide pieces are pre-cemented and not in the form of carbide powder. The specification also states that some cubic boron nitride may be included in the intermediate layer.
U.S. patent application Ser. No. 898,612 now abandoned described a tool component comprising a composite abrasive compact in which the compact layer has two zones joined by an interlocking, common boundary. The one zone provides the cutting edge or point for the tool component while the second zone is bonded to the cemented carbide support. The second zone is produced from a mixture of ultra-hard abrasive particles and carbide particles or ultra-hard abrasive particles coarser than those used for producing the other zone. Since the second zone forms part of the abrasive compact, the ultra-hard abrasive particles present therein, be they diamond or cubic boron nitride, will contain substantial particle-to-particle bonding.